No abstract

A new slip model derived by molecular dynamics has been used to investigate the ultra-thin gaslubricated slider bearings beneath the three bushings of an electrostatic micromotor in micro-electro-mechanical systems (MEMS). Modified Reynolds equation is proposed based on the modified slip model. Analytical solutions for flow rate, pressure distribution, load carrying capacity and streamwise location using the modified Reynolds equation are obtained and compared with the results gained from those in the literature. It demonstrates that the new secondorder slip model is of greater accuracy than that predicted by the first-order, second-order slip models and MMGL model and produces a good approximation to variable hard sphere (VHS) and variable soft sphere (VSS) models, which agree well with the solution obtained from the linearized Boltzmann equation. It is indicated that the slip effect reduces the pressure distribution and load carrying capacity, and shifts the streamwise location of the load carrying capacity, which should not be ignored to study the step-shaped slider bearings in micromotors for MEMS devices.

Among the problems in microelectromechanical systems, friction and wear are the most concerned ones. In this paper, a model to predict the sliding wear between the rotor bushing and the substrate plane in a variable capacitance micromotor is presented. The model is based on the Archard's wear law and takes into account the scale effects, including the effects of such surface forces as meniscus force due to humidity and the electrostatic force as a result of the capacitance coupling between the rotor and substrate, as well as the scale effects of material properties, which become scale dependent in microscale. The wear process and durability of the hemispherical bushing are investigated and discussed. Simulation results show that they are largely affected by these effects, and it is indicated that sufficient attention should be taken in the design and fabrication of micromotors on the scaling effects.